Journal of Materials in Civil Engineering

AASHTO's practice for designing flexible pavements requires resilient modulus of the subgrade soils. The resilient characteristics are assumed to account for the permanent deformations of soils. However, this approach can provide misleading characterizations. Soils such as silty sands, silty clays, and sandy clays possess good resilient characteristics. Nevertheless, they still undergo large plastic deformations under traffic loads. Hence, both elastic and plastic strain responses are necessary for a complete characterization. This paper presents an evaluation on the repeated load triaxial (RLT) test method for providing the permanent strain response of the soils. RLT tests were conducted on three soil types: (1) Well-graded sand; (2) silty clay; and (3) heavy clay. Tests provided the plastic strain data at various confining deviatoric stresses and loading cycles. Data were analyzed with a plastic strain formulation that accounted for stresses and loading cycles. The formulation has reasonably represented the plastic strain response in these soils. Formulation predictions agree with the measured permanent strain results of a field site subjected to accelerated loading. Future research needs are also discussed.

In this work, the effects of the addition of a plant gum, named Astragalus (AS), grown commonly in Central and East Anatolia, Iran, Turkmenistan, and Transkafkasia, on the stability and flow characteristics of asphalt concrete were studied. This material was mixed with asphalt cement in various proportions up to 5%. The relevant measurements were undertaken on the Marshall samples prepared using this mixture and aggregate. It was found that by mixing AS by 2%, a 59% increase in stability could be achieved in comparison with the bitumen without this additive, while considerable increases in the flow values of the asphalt concrete samples, which were still between the acceptable standard limits, were observed with this amount of AS.

Fracture and tensile characteristics of asphalt concrete mixtures affect the structural performance of pavements, particularly under low-temperature conditions. This paper reports a study of the tensile and fracture properties of asphalt-rubber (AR) concrete mixtures that formed the basis for the recommendation of an optimum asphalt mixture design incorporating crumb rubber from scrap tires. The work involved a full-factorial experiment with three different rubber contents (19, 22, and 24%), and three different AR binder contents (6, 7.5%, and 9%) in a surface mixture. Fracture and indirect tension tests were performed on AR concrete beams and Marshall test samples, respectively, at two different test temperatures of 25 and 5°C. The variables studied were indirect tensile strength, peak center-point load carried, load-point displacement, and unit fracture energy. The results show that higher mean values of indirect tensile strength and fracture energy were obtained corresponding to the highest AR binder content (9%), irrespective of rubber contents, particularly at lower temperatures. A statistical analysis of the test results reveals that there are no significant differences among the means of most of the variables studied corresponding to different rubber contents. However, the differences are significant for different binder contents.

Dwindling supplies and rising costs of natural resources used in road construction as well as concerns over shrinking landfill spaces prompt researchers to investigate the use of waste products, such as coal ash, as substitute materials in highway construction. This research examines the effect of coal ash (i.e., fly and bottom ash) when used as partial replacement of fine aggregate in asphalt concrete mixtures. Specimens were made using three aggregate sources, two ash sources, three ash percentages (0, 6, and 8%), and hydrated lime. Selected physical properties (e.g., tensile strength) were measured and statistically analyzed. Results indicated that partial substitution of fine aggregates by coal ash had a moderate detrimental effect on short-term tensile strengths. However, a number of coal ash/lime mixtures met the minimum tensile strength requirements set by the South Carolina Department of Transportation. A limited field study was also conducted to study the environmental effects of coal ash mixtures as detected by heavy-metal concentrations in nearby soils. Results showed that 3 months after placement metal concentrations in soils were not substantially altered.

Sealants used to seal the transverse contraction joints used in joining concrete highway sections without dowels must be flexible enough to withstand excessive conditions such as large temperature fluctuations, severe pavement deflection due to heavy truck traffic, and prolonged moisture exposure. Choosing the most appropriate sealant for the expected service condition from the wide variety of sealants available on the market today can be a daunting task. In Part I of this paper, a comprehensive test protocol that correlates sealant viscoelastic properties with the sealant resistance to deflection is presented. It is proposed that the selection of a sealant should be based on a complete evaluation consisting of three test procedures: (1) the ASTM C794 adhesion-in-peel test to assess concrete/sealant adhesion; (2) dynamic mechanical analysis (DMA) to evaluate sealant flexibility by determining the glass transition temperature, T_g; and (3) the shear fatigue test developed by the writers to analyze sealant performance when subjected to severe pavement deflection in combination with various environmental conditions. Part II of this paper will present the results of testing and comparison of two polyurethane joint sealants using this proposed test protocol.

A comprehensive test protocol, described in Part I of this paper, has been used to evaluate the adhesive strength, viscoelastic properties, and shear fatigue behavior of two polyurethane joint sealants for use in undoweled concrete highway joints. The results of these tests showed that the protocol was able to assist in selecting the more suitable sealant for the expected service conditions in New Brunswick, Canada. Sealant A, a coal-tar modified polyurethane with a glass transition temperature of −20.7°C, showed a significantly reduced flexibility at a severe low temperature of −40°C. This low temperature induced loss in flexibility was supported by the relatively low peel force required to initiate cohesive failure and the relatively high resistance to shear deflection noted with the shear fatigue test. Sealant B, on the other hand, was found to have a glass transition temperature of −43.2C and maintained its flexibility at extreme low temperatures for all dynamic tests performed. Using dynamic mechanical analysis, neither sealant showed significant degradation at high temperatures or when subjected to water or ethylene glycol exposure.

An experimental study was carried out to assess the mechanical properties of high-performance pastes and mortars reinforced with steel microfibers. Two series of mixtures were made with three microfiber contents (0, 2.5, and 5% of the paste volume), three sand-to-binder ratios (S/B = 0, 1, and 2), and three sand gradings. In the first series, 21 mixtures were batched under vacuum to avoid air entrainment. In the second series, 10 additional mixtures were batched with and without a defoaming admixture. After 14 days of curing, compressive tests and third-point loading flexural tests were carried out on paste and mortar specimens. Tensile tests were also carried out after a 3-month curing period. The results obtained indicate that the batching of mixtures under vacuum and the use of a defoaming admixture were found to be two efficient ways to significantly lower the air content in microfiber reinforced mortars. They also reveal that the addition of microfibers significantly improves the mechanical properties of the cement pastes but provides only little improvement for the mortars.

The influence of a woven fabric structure on the flexural behavior of cementitious composites was studied. The fabrics used were all plain weave with different fills densities of 5, 7, or 10 fills per cm and the warps density was kept constant (22 warps per cm). The yarns were all monofilament from polyethylene. The crimped geometry of the individual yarn in the fabric might influence the bonding between the matrix and the fabrics and the overall performance of the composite. Two different types of composites were prepared: (1) Samples with fabrics; and (2) samples with crimped yarns that were untied from the fabrics. Three different tests, flexural, tensile, and pullout, were carried out to characterize the mechanical performance of the composite and the bond between the fabrics and the matrix. Special attention was given to the characterization of multiple cracking, which may contribute to the understanding of the bonding between the fabrics and the matrix. It was found that the fabric structure, which yields a high bond, did not provide a composite with better properties than in the case of crimped untied yarns. Weakening of the matrix due to less efficient compaction was detected as a significant parameter. When fabrics are used, the compaction is less efficient and the performance is poorer. The lower stress magnitude for first crack appearance supports that observation.

In this paper the results of tests performed on specimens and structural elements made of steel fiber reinforced concrete (SFRC) are presented. Fiber content of the concrete ranged from 0 to 60 kg/m³. Using the results of the uniaxial compression tests performed under displacement control condition, a stress-strain relationship for fiber concrete in compression was derived. Three-point bending tests on notched beams were carried out to simulate the postcracking behavior and to evaluate the fracture energy. Based on the constitutive relationships derived from the experiments, a layered model for the analysis of steel fiber reinforced concrete cross sections was developed. The model performance and the benefits of fiber reinforcement on thin slabs reinforced with steel bars were assessed by carrying out tests on slab strips. The main results are presented and discussed.

The biogenic corrosion of mortars by sulfuric acid-producing bacteria was simulated in a controlled breeding chamber. Calcium aluminate cement (CAC) as well as portland and blended portland cement mortars were tested. Growth conditions for bacteria were optimized in a way that accelerated the naturally occurring corrosion (worst case) by a factor of at least 24. After 12 months of incubation in the chamber the samples being tested could be clearly classified according to their resistance properties. CAC mortars were found to resist microbiologically induced corrosion significantly better than portland and blended portland cement mortars. Measurement of the amount of biogenic sulfuric acid on CAC and portland and blended portland cement mortars demonstrated a higher amount of acid on the latter. The more effective resistance of CAC mortars was explained by the higher neutralization capacity due to their chemical composition and the smaller production of biogenic acid. Chemical immersion tests in sulfuric acid at pH 2 also revealed better resistance properties for the CAC mortars. But the mortars could not be distinguished as well as in the biological test because the samples were all exposed to the same concentration of acid. It is concluded that predictions concerning the long-term behavior of mortars used in sewerage networks are only reliable on the basis of the biogenic simulation experiment because the different metabolic activities of sulfuric acid-producing bacteria inhabiting different materials should be taken into account. Chemical corrosion tests tended to overestimate the resistance properties of portland and blast furnace cement mortars.

Brittle failures are frequently encountered in wood bolted connections. Because of high localized stress concentrations, cracks initiate at the boundary of the bolt-hole and propagate parallel to the grain. This paper is intended to examine the attributes of fracture mechanics in predicting the brittle failure of such structural joints under short-term loading. Models proposed for wood and fiber-reinforced composites are reviewed. Then solution techniques for the stress analysis and failure criteria of connections are presented with typical examples from literature. It is found that several conditions must be considered simultaneously in the analysis. These are the geometric nonlinearity due to sliding contact, the material nonlinear behavior before and after fracture, and the fastener deformation in the plane parallel to the bolt axis in the case of connections between thick members. As yet, there is no failure theory for bolted joints in orthotropic materials with general applicability. Fracture mechanics models are more appropriate than strength criteria as tools for predicting brittle failures. They should, however, be applied with caution by identifying the fracture parameters that control the initiation and stable propagation of cracks until ultimate failure.

Lining of underground pipeline networks with deformed/reformed high-density polyethylene (HDPE) liners is a trenchless technique frequently specified for rehabilitation. According to the current design practice, a liner can be structurally designed as a flexible pipe, rigid pipe, or composite pipe, depending on installation conditions. One of the most important design considerations of a confined liner is its buckling under a uniform pressure similar to that exerted by ground water seeping through the deteriorated host pipe. Because long-term testing of a lining system is both time-consuming and expensive, it becomes extremely important to establish a design criteria for long-term conditions more quickly and economically. In the reported study, over 200 short-, medium- and long-term tests were performed to examine the effects of the diameter, thickness, and deformities on the buckling characteristics of a HDPE liner pipe. Based on the findings of the study, some recommendations were proposed for the design and testing of plastic liners under short- and long-term loading conditions.